HR: 0830h
AN: NS41B-09    [Abstracts]
TI: Complex Impedance of Swelling and Non-swelling Clay-Brine Suspensions
AU: * Sweeney, J
EM: sweeney3@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Avenue PO Box 808, L-201, Livermore, CA 94551 United States
AU: Roberts, J
EM: roberts17@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Avenue PO Box 808, L-201, Livermore, CA 94551 United States
AB: We carried out electrical impedance measurements over the frequency range of 1 Hz to 1 MHz on mixtures of swelling and non-swelling clay samples in NaCl solutions ranging from zero to 0.35 molar. The purpose of the measurements was to try to identify possible differences in the impedance response of the two clays under controlled conditions that could be exploited in the field. Measurements were carried out using a two-electrode liquid test fixture; the electrode gaps and applied voltages were varied to assure that these parameters did not affect the results. For the mixtures of 1g/L dispersed clay in the solution, no flocculation or settling occurred during the measurements. For both clays, the d.c. conductivity follows Archie's Law down to very low brine concentrations [0.001 molar - 0.01 S/m for Na-montmorillonite (swelling) clay; 0.0001 molar - 0.001 S/m for kaolinite (non-swelling) clay]. At lower NaCl concentrations the conductivity of the mixture is constant at a level consistent with the relative cation exchange capacity of each clay. For a dispersed clay mixture in brine, once the brine concentration exceeds the threshold conductivity, both the d.c. and complex conductivity is the same as that of a pure brine solution and the clay mixtures are indistinguishable. This change in conductivity behavior occurs at brine concentrations below those typically encountered in nature. This work was performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory under contract W-7405-ENG-48 and supported specifically by the Office of Basic Energy Science.
DE: 1899 General or miscellaneous
DE: 3914 Electrical properties
DE: 5109 Magnetic and electrical properties
SC: Near-Surface Geophysics [NS]
MN: 2005 Joint Assembly